While I'm not going to waste time trying to figure out how to implement the Structured Data HTML, the Data Highlight Tool is easy to use and makes it easy to highlight certain portions of your site for appearing in the search results.
However, could highlighting the "wrong" stuff end up hurting you in the search results?
I'm already in a great spot for a few of my sites, and I feel like messing around with stuff, who knows what could happen.
I did use the Data Highlight Tool and I feel I highlighted something that would only HELP my site as it appears in the results, but you damn well never know with this stuff.
I suppose that highlighting "the wrong stuff" might cause a problem. Any incorrect use of technology can casue problems, including HTML itself.
That said, you're the first person I know of who is actually using the tool, so I can't report on the real world experience very well. If your site holds structured data, it sounds like it might be useful.